Instrument Cluster Problems

[Walt in Asheville]

Hello all,

I would like to know a plan of action for the following issues:

1. All four needles are no longer viewable. I assume this is due to some sort of flouresent paint on these needles and aging.

2. The speedometer is inop. It waivers around at 20 mph. I am wondering if this is a computer issue or if there is a physical connection that is faulty.

Thanks in advance,
Walt

[fhb5032]

Apparently a very common problem. My recently purchased '93 sc400 has a dead speedometer needle.and flickering tach needle. There are several re-builders on e-bay who use LEDs that don't die.

Can't comment on their reliability, but they are out there.

Other possibility is a used one from a "re-cycler" AKA junkyard. But then you face the same problem again.

[fhb5032]

Oh, I should have noted that the needles are illuminated, and the illumination is what's failing not luminous paint.

[Walt in Asheville]

Can anyone offer some insight on this part of the issue????

"2. The speedometer is inop. It waivers around at 20 mph. I am wondering
if this is a computer issue or if there is a physical connection that is
faulty."

[fhb5032]

I really doubt that it is mechanically driven by a cable. given how much these cars are automated with sensors at each wheel, the drive shaft and transmission, but, I don't know for sure. On the other hand, it's hard to figure how a sensor/computer problem would create the wandering needle characteristic of the old spinning magnet on a cable mechanism.

I do have shop manuals. If I get a chance tomorrow and no one has posted an answer by then, I'll research how the speedometer operates and post what I learn.

[Walt in Asheville]

fhb5032,

thanks for that. I appreciate it.

The needle seems to stay around 20 mph and varies at times from zero to about 35. Looking at its behavior it looks like there is a bad sensor somewhere in the system. If you could, find out where that speedo sensor is and if they have testing specs that the sensor should show if I put an ohm meter to it.

Regards,
Walt

[fhb5032]

If the needle is that erratic, then it's probably not the sensor - since that sensor is probably working for the computer also. That much intermittent operation would almost certainly set a code. I've had a TRAC or ABS code set if one of the tires has low air pressure.

It sounds like an intermittent problem with what ever mechanism is driving the needle movement. So it would be in the instrument cluster.

I will try to find time to check the book and let you know.

[Tomcat07]

Re: the fading instrument lights. I had the same problem on my 95' SC400. My local repair place (Import Auto) ordered 7 cluster lights from the Lexus dealer and installed them . The cost including labor/parts was $160.00.

[dcfish]

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CC8QFjAA&url=http%3A%2F%2Flextech.org%2F&ei=08h3Ur2tL4v2qwHC4YHgCA&usg=AFQjCNGxXqgpBU4z8mzhmF135-tJZPliBw&sig2=3WNf_0rwOzCS4lr3G9Whgw&bvm=bv.55819444,d.aWM

[Walt in Asheville]

Upon further observation I note that the speedo needle is NOT erratic. It seems to move up and down logically with speed. It simply has a range of up to 20mph with my normal driving. With 20MPH being what is showing when I am at Interstate Speeds.

[fhb5032]

All the data comes in from the computer as far as I can tell from the wiring diagrams and related stuff.

It must be an electromechanical problem in the cluster.

[cduluk]

How long have you had the car? Did the needles quit illuminating all at once, or did they gradually burn out?

Each needle is illuminated by several (maybe 20 or so) tiny tiny SMDs (surface mount diodes, similar to LEDs) placed in a row within the needle itself. Due to poor engineering, the SMDs are given too much voltage and current, causing them to heat up when in use. Over time, the heat causes them to burn out. They usually start flickering, one section at a time. There's no cure, only replacement--OEM or aftermarket. There are people on eBay who offer aftermarket fixes. They usually look like crap, however.

In re: to the speedo needle only ranging between 0 and 20mph, it could be a number of things. The needles themselves are driven by stepper motors which receive electricity sent by the car's computer, which receives messages from sensors. Attached to the pin coming out of the stepper motors is a "coil" that delivers voltage from the cluster circuit board to the needles for needle illumination. If this coil has dirt built up on it, it might be restricting the range of the needle-but i doubt it. My bet is on the sensors or on the stepper motor itself.

In any case, you're gonna need another cluster. I'd buy a used one from ebay (with working needles) and see if the speedo works. If so, you know the cluster is to blame. If it still doesn't work, you know there's an issue with the car's sensors or main computer.